Tropical Highlights -
Current atmospheric and oceanic conditions continue to reflect neutral
conditions across the Tropical Pacific (Tables T1,
T2). Sea surface
temperatures (SSTs) remained slightly warmer than average across the western
and west-central Pacific and were slightly cooler than average along the
South American coast (Fig. T18). SST anomalies more than 1°C
above normal have persisted in the equatorial west Pacific since July (Fig.
T9). SST anomalies in the four Niño
regions have exhibited little change since July (Table
T2, Fig. T4).
Oceanic thermocline depths, as measured by the depth of the 20°C
isotherm (Figs. T15, T16) was slightly deeper than average across
most of the equatorial Pacific during September. Consistent with these
conditions, oceanic temperatures at thermocline depth were 1-2°C
above average across most of the equatorial Pacific (Fig. T17).
Both the low-level and upper-level equatorial winds were near average
across the Pacific during September (Table T1, Figs.
and the Tahiti-Darwin SOI also remained near zero (-0.1) during the month (Table
T1, Fig. T1). None of these indicators has exhibited any trend towards
warm or cold episodes during the past four months and all are consistent
with near neutral conditions across the Tropical Pacific.
Relatively weak outgoing longwave radiation (OLR) anomalies were again
observed throughout much of the global Tropics during September, with the
largest negative anomalies observed over the western Pacific (Fig. T25).
Enhanced convection (negative OLR anomalies and above-average precipitation)
was observed over north-central India (Fig. T25) and also over the
west African Sahel (Figs. E3, E4). Rainfall was above-normal over the
African Sahel during all four months of its rainy season (Fig. E4).